Role of CRP-positive cerebellar climbing fiber system in the development of vestibular compensationThe present immunohistochemical study demonstrated an increase in number of corticotropin-releasing factors (CRF)-positive mossy and climbing fiber terminals in the vestibulocerebellum in an ataxic mutant, rolling mouse Nagoya (RMN). Unipolar brush cells (UBCs), a class of interneurons in the vestibulocerebellum, amplifies excitatory inputs from mossy fibers. The number of calretinin (CR)-positive UBCs in the vestibulocerebellum was no different between RNM and the control mice. But, the number of CFR-positive mossy fiber terminals in closely apposition to CR-positive UBCs was 5-fold greater in RMN than in the controls. It is suggested that CRF-positive mossy fiber terminals in contact with UBCs in the vestibulocerebellum compensate the cerebellar ataxia in RMN.An attempt was made to clarify the roles of CRF-positive mossy fiber terminals in contact with UBCs in the vestibulocerebellum in the development of vestibular compensation. After unilateral labyrinthectomy in mice, there were no changes in number of CRF-positive mossy fiber terminals in contact with UBCs in the vestibulocerebellum. Although the number of CRF-positive climbing fiber terminals was increased in the vestibulocerebellum of RMN, there were no changes in number of CRF-positive climbing fiber terminals in the vestibulocerebellum after unilateral labyrinthectomy in mice. All these findings suggest that CRF-positive mossy and climbing fibers in the vestibulocerebellum do not play roles in the development of vestibular compensation.On the contrary, the number of CRF-positive terminals in the ipsilateral medial vestibular nucleus was decreased after unilateral labyrinthectomy in mice, suggesting that CRF affects the development of vestibular compensation in the vestibular nuclei, but not in the vestibulocerebellum.